Typical rubber hoses, for example, made of a blend of acrylonitrile-butadiene rubber and polyvinyl chloride (NBR/PVC blend) which is excellent in resistance to gasoline permeability, have been used for conveying fuel (fuel such as gasoline for engine) for automobiles or the like in view of their high vibration-absorbability, easy assembling or the like. However, for the purpose of global environment protection, the regulations have been recently tighten against permeation of fuel for automobiles or the like, and are anticipated to be further tighten in the future. Therefore, such hoses for conveying fuel are required further permeation resistance to fuel.
And, hoses for conveying fuel such as hydrogen gas used in fuel cells, or for conveying carbon dioxide gas refrigerant are required extremely high permeation resistance to such conveyed fluid as hydrogen gas, carbon dioxide gas.
However, with regard to this requirement hoses configured by organic materials only such as rubber or resin are difficult to satisfy such required resistance.
Under the circumstances, it is considered to form preferably a composite hose by combining with a corrugated metal tube as a barrier layer against permeation of conveyed fluid.
For example, U.S. Pat. No. 6,354,332 discloses a composite hose with a corrugated metal tube of this type.
Meanwhile, when an internal pressure is exerted to such composite hose with a corrugated metal tube repeatedly, the corrugated metal tube suffers a large stress, and there is a fear that thereby the corrugated metal tube is fatigue-cracked at an early stage.
In order to prevent such fatigue-crack, the composite hose with a corrugated metal tube is preferably provided with a reinforcing layer in order to restrain the corrugated metal tube from deformation in longitudinal and radial directions by providing longitudinal and radial constrain with the corrugated metal tube.
Then, the inventors of the present invention manufactured a sample of composite hose with a corrugated metal tube which includes one reinforcing layer mainly for reinforcing in a longitudinal direction and the other reinforcing layer mainly for reinforcing in a radial direction, and evaluate the sample.
FIG. 7 shows one example thereof as comparison example.
With reference to FIG. 7, reference numeral 200 indicates a composite hose with a corrugated metal tube (hereinafter just referred to as a hose), which includes a corrugated metal tube 202 as an innermost layer by way of a barrier layer against permeation of conveyed fluid. A radial outer side of the corrugated metal tube 202 is laminated in sequence with a rubber filler layer 204, a first reinforcing layer 206, a middle rubber layer 208, a second reinforcing layer 210 and an outer surface rubber layer (cover rubber layer) 212.
Here, the first reinforcing layer 206 carries a function for pressure resistance when an internal pressure is exerted. The first reinforcing layer 206 is formed by braiding reinforcing thread made of organic fiber, at a braid angle or braiding angle larger than a neutral angle (about 55°).
The first reinforcing layer 206 serves mainly to restrain the hose 200 entirely from deforming in an expanding manner when an internal pressure is exerted.
The expansion restraint effect acts also on the corrugated metal tube 202. And, the first reinforcing layer 206 serves to restrain the corrugated metal tube 202 from deforming in an expanding manner when an internal pressure exerted.
On the other hand, the outer second reinforcing layer 210 mainly serves to restrain the hose 200 from dimensional change in a longitudinal direction, namely deformation in the longitudinal direction. Here, the second reinforcing layer 210 is formed by braiding a reinforcing wire member or filament member made of a metal wire, at a braid angle smaller than the neutral angle.
However, a durability test was conducted where an internal pressure is exerted repeatedly at intervals to the hose 200 which is bent into a U-shape (actually, a hose for automobile use, etc. is often equipped in such a bent form). And, it was found that the hose 200 does not necessarily have sufficient durability.
Then the hose 200 to which the test was conducted is examined with regard to its fatigue-cracked area. And it is recognized that the hose 200, specifically the corrugated metal tube 202 was dimensionally changed, namely deformed excessively in the longitudinal direction resulting in the fatigue-crack initiation at early stage.
From this test result, the inventors estimated that the second reinforcing layer 210 did not have a sufficient effect to restrain deformation in the longitudinal direction, and prepared another sample of the hose 200 including the second reinforcing layer 210 where a braid density or braiding density is increased. Although a durable life of the hose 200 was expected to be prolonged, it was decreased after all.
Then, the inventors pursued the cause why the durability of the hose 200 is lowered after all by forming the second reinforcing layer 210 by braiding the reinforcing wire member made of a metal wire at increased braid density, and recognized in pursuit of the cause the fact that thus formed second reinforcing layer 210 debonded and separated itself from an adjacent rubber layer on an inner peripheral side of the U-shaped bend thereof, so-called dropout phenomenon occurs.
When the second reinforcing layer 210 debonds and separates itself in such manner, as a matter of course, sufficient reinforcing effect is not provided by the second reinforcing layer 210.
Although in this way the second reinforcing layer 210 separates itself at a portion on the inner peripheral side of the U-shape bend thereof when the durable test is conducted by exerting an internal pressure to the hose 200 which is bent into a U-shape, the reason for that is regarded as follows.
The second reinforcing layer 210 is formed from a reinforcing wire member made of a metal wire. Therefore, the second reinforcing layer 210 has very large rigidity compared to that formed from a reinforcing thread made of an organic fiber. So, as shown in FIG. 8(A), when the hose 200 is sharply bent into U-shape, a force is exerted to the metal wire in an axial and compressing direction on an inner peripheral side of U-shape bend, i.e., on a contracting side in a longitudinal direction. On the other hand, at a portion on an outer peripheral side of the U-shape bend, namely on an expanding side in a longitudinal direction, a force is exerted thereto in a pulling direction. As a result, a force is exerted to the metal wire downwardly as shown by an arrow in FIG. 8(B). Then, the metal wire cannot bear the force, debonds and separates itself from an adjacent rubber layer downwardly in the figure. Consequently, drop-out phenomenon seems to occur as shown in FIGS. 9(A) and (B), more specifically there seems to occur the phenomenon that the metal wire, namely the second reinforcing layer hangs downwardly on the inner peripheral side of the U-shape bend thereof.
And, the higher braid density of the metal wire the second reinforcing layer 210 has, the more the phenomenon seems to be promoted.
The reason that the durability of the hose is lowered after all when the braid density of the metal wire is increased seems due to this fact.
The present invention is made under the foregoing circumstances. It is an object of the present invention to provide a composite hose with a corrugated metal tube wherein although a reinforcing layer is formed by braiding a reinforcing wire member made of a metal wire, the reinforcing layer does separate itself, offers favorably an effect of restraining the composite hose from being deformed in a longitudinal direction, and thereby a favorable durable life is provided.